Need help about IP Addresses

Is the server a shared hosting setup or something else? If you've got full control of the server then the easiest thing to do would probably be to use a firewall that only allows traffic from your office network.

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Will I get a better result on a public host? 

Yes and maybe. You might not always get the "real" ip as there could be a proxy server in the chain. But you should be able to tell if what you're getting is in the range of IP addresses used by your office network.